1. Field of the Invention
The present invention relates to medical imaging systems and more particularly to Positron Emission Tomography (PET) scan systems and methods.
2. Related Art
Medical imaging systems are used in the diagnosis and treatment of patients. They are non-invasive and therefore are considered safer than surgical procedures to examine internal body tissue.
Positron Emission Tomography (PET) is an imaging technique which enables visualizing the three-dimensional distribution of radionuclides in the human body. For example, a radiopharmaceutical containing suitable short-lived cyclotron-produced radionuclides, such as carbon eleven or nitrogen thirteen in a glucose solution, is injected into the subject to determine varying metabolic rates in the different areas of the subject's brain. The subject is placed in a PET scanner. The radionuclides undergo decay with spontaneous emission of positrons. The positrons combine with a nearby electron to simultaneously generate two photons by annihilation, which travel in opposite directions along a line, i.e., anti-parallel. The two photons are detected as light flashes by two scintillation detectors positioned on opposite sides of the patient. The number of coincidences of detection (electronic collimation) by the detectors may be viewed as the degree of intensity at each pixel of images constructed by a computer system associated with the PET scanner.
Generally, the PET scanner produces a series of images corresponding to parallel planes ("slices") through a portion of the patient's body, for example, 14 slices of the brain. The physician may view the slice images, for example, to determine areas of abnormal metabolic activity.
However, the amount and accuracy of the information obtained by the physician depends upon his training, ability and attention. Some of the information content present in the PET scans may be missed, even by experienced personnel, because the image intensity variations are too slight or too gradual to be detected by eyesight, or lie within the statistical variability of the counting rate of the radioactive decay (approximately 1 .sqroot.n, where n is the number of radioactive disintegrations per pixel per unit time) or lie within the normal variability encountered from individual to individual.